Circuit arrangements for producing substantially constant currents



May 31., 1960 D. s. RIDLER L 2,939,019

CIRCUIT ARRANGEMENTS FOR PRODUCING SUBSTANTIALLY CONSTANT CURRENTS Filed Dec. 19, 1955 2 s n i /]I IL/CUFF?! I LOO resistance L0 00 current Primary seconobr) currents current INVENTOP D. S. RID L ER A 7'7'ORNE Y United States Patent "ice CIRCUIT ARRANGEMENTS FOR PRODUCING SUBSTANTIALLY CONSTANT CURRENTS Desmond Sydney Ridler and Robert Grimmond, London, England, assignors to International Standard Electric Corporation, New York, N.Y.

Filed Dec. 19, 1955, Ser. No. 554,074

Claims priority, application Great Britain Dec. 31, 1954 3 Claims. (Cl. 307-106) The present invention relates to constant current sources.

. According to the present invention there is provided a circuit arrangement for producing an electrical current of substantially constant amplitude which comprises a core of a ferro-magnetic material having a substantially rectangular hysteresis loop, which core is normally in a condition of remanence in one direction of magnetisation, a winding on said core, and means for applying a voltage across said winding in such a direction and of such a magnitude as to drive said core towards saturation in the other direction of magnetisation, whereby a current ofsubstantially constant amplitude flows in said winding while said core is changing its condition along the corresponding vertical porton of said loop towards saturation in the other direction of magnetisation.

The invention will now be described with reference to the accompanying drawings, in which:

Fig. l is an idealised hysteresis loop of a so-called square-loop ferro-magnetic material, the product of flux and time being plotted against the product of magnetisation and current, I

Fig. 2 is an idealised representation of how the current flowing in a coil wound on a core having a hysteresis loop such as that shown in Fig. l varies, current being plotted against time. The inset to the figure shows the circuit.-

Fig. 3 is a representation similar to Fig. 2 of the current flowing when the core has a secondary winding in which a load current can flow, the circuit being shown as an inset to the figure.

Fig. 4 is a circuit diagram of an extension of the principle exemplified in Fig. 3 wherein a winding on a second core is connected in series with the primary winding.

Fig. 5 shows how the load current in the circuit of Fig. 4 varies with the load resistance.

Fig. 6 shows three cores having primary windings interconnected in series, the secondary windings not being so interconnected. This circuit is used to produce a series of three staggered pulses in the three secondary windings.

Fig. 7 shows how the primary and secondary currents vary with respect to time in the circuit shown in Fig. 6.

In the ensuing description the two directions of magnetisation to either one of which a ferro-magnetic core can be set are referred to respectively as the negative and positive directions of magnetisation. Initially it will be assumed, see Fig. 1, that a core is left in a state of negative remanence, i.e. in the condition indicated at at which the core is negatively magnetised but is not saturated.

The state of the core can be changed from negative remanence to positive saturation by applying a voltage of suitable polarity and amplitude across a winding on that core. In the ideal case, as can be seen from Fig. 1, the current flowing in the winding rises almost instantaneously until the first knee 1 of the. hysteresis 2,939,019 Patented May 31, 1960 loop is reached, whereafter the current flowing remains substantially constant as the condition of the core negotiates the vertical portion of the hysteresis loop until the second knee 2 of the hysteresis loop has been reached. Thereafter the current commences to rise again, theoretically rising to infinity. The current time relationship of the circuit is shown in the inset to Fig. 2.

In this circuit, although the current flowing in the winding remains constant for a period determined by the time which the core takes to reach the second knee 2 from the first knee *1, the flux in the material of the core is changing throughout this constant current period. This follows from a perusal of Fig. 1 which shows that during the period of constant current, the product of flux and time is constant, so that clearly the flux must be changing. The importance of this changing flux will become apparent in due course.

The current is constant during the period of the kneeto-knee transition along the vertical portion of the loop because during this period the slope permeability of the core material changes from the very low value which applies at the remanence point to a very high value. The duration of the constant current is given by t 10 secs.

where n is the number of turns on the winding, gi is the remanent flux, is the saturation flux, and V is the applied voltage across the winding.

Clearly, if the applied voltage is removed from the winding before the core has saturated, the core returns to negative remanence, so that the core acts as a constant current supply for the duration of the voltage across its winding.

If a secondary winding is placed on the core, as shown at 3 in the inset to Fig. 3, the device will operate as a transformer and an will be induced in the secondary winding to which a load 4 may be connected. This will only be present while the flux is changing in the core, i.e. during the period of the knee-to-knee transition. As can be seen from the hysteresis loop shown in Fig. 1, there is little or no flux change before the first knee or after the second knee. Any current absorbed by the load 4 connected to the secondary winding 3 will then appear as an additional current flowing in the primary circuit, the value of this additional primary current being dependent on the primary-to-secondary turns ratio.

There again if the input voltage ends before the core saturates, the core reverts to negative remanence so that the secondarywinding current is a pulse whose length equals the duration of the primary winding voltage.

The circuit shown in the inset to Fig. 2 has an additional winding *5 connected in series with a battery and a switch 6, so that when the switch 6 is closed a current flows through the winding in such a direction as to return the core to its negatively magnetised state. Hence when the switch 6 is opened, the core is left at negative remanence Fig. l. A similar additional winding 5 is shown on the core in the inset to Fig. 3. Of course no provision for resetting would be needed it the circuit is so used that the core does not saturate. These switch and battery combinations for resetting the cores, and the switch and battery combinations shown for producing the transitions from to would normally be electronic circuits, but have been shown as switches and batteries in the interests of simplicity.

While a core is being returned from its positively magnetised state to its original negatively magnetised state there will be a further period while the core is negotiating the other vertical portion of the loop, i.e. the vertical portion between the other two knees of the curve, during which a constant current flows in the w nding across which the resetting voltage is applied. This second constant current period may be of practical use, but

if its presence in the secondary circuit feeding the load 4 (Fig. 3) is undesirable, blocking means, for instance a rectifier 7, may be included.

The resetting could also, of course, be effected by a current flowing in the original or primary winding on the core in the opposite direction to the current causing the to transition.

The value of the load current can be limited by limiting the current flowing in the primary winding on the core. To do this, a second core also having a rectangular hysteresis loop is used with a winding on it connected in series with the primary winding of the first core. in Fig. 4 the second core is shown at 8, and the first core at 9. The flux change in the second core is arranged to occur at a value of current at least equal to that which saturates the first core. This can be achieved, for example, by increasing the magnetic path length of the second core as compared with that of the first core, or by reducing the number of turns on the winding on the second core if the second core is to saturate at a higher current than the first core. Furthermore, the time taken for the second core to change from one polarity of flux to the other is comparatively long. This can be achieved by increasing the cross-sectional area of the core.

Given the conditions set out in the preceding paragraph, i.e. that core 8 changes over at a value of current at least equal to that which saturates core and also takes longer to change over, and asurning that the flux transition occurs at a current I in the primary winding of the first core 9, and at I in the winding on the second core 8, and that the primary-secondary turns ratio of the first core is N :N If the voltage is now applied to the two cores, the maximum current which can flow in the primary winding of the first core is I whatever the value of the load, since the current is limited to a constant value by the second core before the latter saturates.

This assumes also that both cores are returned to their original state, i.e. negative remanence, after each operation, for instance by the use of an extra resetting winding on each core, as shown in insets to Figs. 2 and 3, or by passing a reverse current through the series-connected windings on cores 8 and 9. The resetting arrangements, being similar to those used in the above-described circuits, are omitted from Fig. 4. The assumption is further made that the voltage applied to the cores 8 and 9 is removed before the second core has had time to saturate. Hence the circuit produces, in the secondary winding on core 9, a pulse of current Whose duration depends on the characteristics of core 9, which pulse is of substantially constant amplitude for a wide range of load values. The relation between load resistance and load cur ent is shown in Fig. 5, and it will be seen that when theload resistance exceeds a certain value, the current commences to fall. A possible application of the circuit of Fig. 4 would be the production from a master pulse of a pulse of shorter duration and of defined amplitude. For this purpose it would be arranged that the first core 9 commences to traverse the vertical portion or" the loop at the current value at which the secondary current has the desired amplitude and that the time taken to traverse the vertical portion gives the duration of the desired pulse. The second core 8 saturates at a current value equal to or greater than the first core and its time to traverse the vertical portion of its core exceeds the duration of the master pulse.

The arrangement shown in Fig. 6 is an extension of the principle of Fig. 4 to the production or" a series of three staggered pulses. Such series of two or more pulses are used to operate certain varieties of pattern movement or shifting registers and counters. These pulses can be produced by a series of cores 10, 11 and 12 respectively having their primary windings interconnected in series, with the secondary windings forming the separate outputs from the circuit. The separate cores change over at successively higher values of current, and take successively longer periods to do this. Hence by suitably proportioning the cores and the windings there on, the current in the primary circuit, has the characteristic shown in the upper portion of Fig. 7. The broken lines show the open circuit current, while the solid lines show the currents which flow with the respective secondary windings feeding load circuits.

As will be apparent, assuming that the cores saturate in the order ltil1ll2, when core 10 saturates, the current flowing in the secondary winding thereof ceases because the saturation of the core has stopped the flux therein from changing. Core 11 is so proportioned that the knee-to-knee transition commences just as core 10 saturates, and the flux change during its transition causes the production of the second pulse, which ends when core 11 saturates. The output pulse from the secondary of core 12 is produced in a similar manner.

Obviously some current limiting device, for instance a core with winding such as core 8 in Fig. 4, is necessary in series with the cores 1t), 11 and 12 in Fig. 6 to prevent an excessive current from flowing. Further, some resetting arrangements for the cores in Fig. 6 is necessary. These have been represented as a battery and switch in series with additional windings on the cores.

It will be seen from Fig. 7 that the current flowing in the circuit of the primary windings of the cores 10, 11 and i2 is of a stepped waveform. If such a waveform is required, the simple addition to the primary circuit of an output circuit for this waveform could be made.

Considering the circuit of Fig. 6, it would be possible to arrange that a number of cores commence their transition along the vertical portion of their hysteresis loops at the same value of current, but which take different times to complete their transitions. In this case the outputs obtained in the respective secondary windings would be a set of pulses starting at the same time but ending at different times.

In the circuits described above in which a core has its own secondary windings, the core with its windings can be regarded as a switch which connects an output circuit connected to the secondary winding to the power supply for a defined period during which current flows in the output circuit. Similarly, a train of cores, such as is shown in Fig. 6, can be regarded as a distributor interconnecting the power supply and the respective outputs singly and successively for defined periods.

It must not be forgotten when using the circuits embodying the present invention that the waveforms shown are idealised, and that they would in practice depart from the ideal by an extent which depends on the departure from the ideal of the hysteresis loop of the core material.

While the principles of the invention have been described above in connection with a specific embodiment, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

l. A circuit arrangement comprising a first core of ferro-magnetic material, a second core of ferro-magnetic material having a substantially rectangular hysteresis loop, means for normally causing both said cores to assume a condition of remanence in one direction of magnetization, a primary winding on said first core, a secondary winding on said first core, a load circuit connected across said secondary winding, a primary winding on said second core connected in series with said primary winding on said first core, a source of voltage, the relative shapes of the hysteresis loop of said first and second cores being such that the primary ampereturns required to drive said first core from its remanent condition to a point of zero flux is less than that for said second core and the flux required substantially to saturate said first core is greater than that required to saturate said second core, and switch means for applying a voltage from said source to said primary windings of such polarity and magnitude as to drive said first and second cores towards saturation in the other direction of magnetization without saturating said second core, whereby a substantially-constant current flows in said secondary winding and said load circuit as a result of applying said voltage for a limited time.

2. A circuit arrangement, as defined in claim 1, in which the first core has a rectangular hysteresis loop, further comprising a secondary winding on the second core and a load circuit across said last-mentioned secondary winding, the characteristics of said cores being such that the transitions along the respective vertical portions of the hysteresis loops of said cores towards saturation in the secondary direction of magnetization commence at suc- 3. A circuit arrangement, as defined in claim 2, in which there are more than two cores each having a primary winding and a secondary winding and a load circuit connected across each secondary winding, the primary windings being connected in series, the characteristics of said cores being such that the transitions along the respective vertical positions of the hysteresis loops of said cores towards saturation in the second direction of magnetization commence at the same value of current but take inereasingly longer times, whereby the currents which flow in the secondary windings of said cores form a series of pulses which start at the same time but which have successively greater duration, each said pulse lasting for the period of transition of the respective core.

References Cited in the file of this patent UNITED STATES PATENTS 2,375,609 Zuhlke May 8, 1945 2,719,773 Karnaugh Oct. 4, 1955 2,730,694' Williamson Jan. 10, 1956 2,758,221 Williams Aug. 7, 1956 2,781,504 Canepa Feb. 12, 1957 

